Method for controlling electronic expansion valve of air conditioner

ABSTRACT

A method for controlling an electronic expansion valve (EEV) in an air conditioner using a compressor includes the steps of: (a) opening the EEV completely when a power is applied to the air conditioner in stand-by mode; (b) closing the EEV completely when the air conditioner starts a cooling or a heating operation; (c) calculating an indoor heat load; (d) calculating a reference opening pulse frequency of the EEV; and (e) controlling in a stepwise manner an opening pulse frequency of the EEV based on the reference opening pulse frequency of the EEV. The opening pulse frequency of the EEV is controlled in a stepwise manner until it reaches the reference opening pulse frequency of the EEV.

FIELD OF THE INVENTION

The present invention relates to an air conditioner; and, more particularly, to a method for controlling an electronic expansion valve (EEV) of an air conditioner, which is suitable for controlling an opening level of the EEV that is installed between an outdoor heat exchanger and an indoor heat exchanger to adjust an amount of refrigerant to be circulated.

BACKGROUND OF THE INVENTION

As known well in the art, a typical air conditioner has a structure illustrated in FIG. 1.

Referring to FIG. 1, the typical air conditioner is largely divided into an outdoor unit 110 and an indoor unit 120. The outdoor unit 110 includes a compressor 111, a four-way valve 112, an outdoor heat exchanger 113, an electronic expansion valve (EEV) 114, an accumulator 115 and an outdoor fan 116. The indoor unit 120 includes an indoor heat exchanger 121 and an indoor fan 123.

During a cooling operation of the typical air conditioner with the above-described configuration, a high-temperature and high-pressure gaseous refrigerant compressed in the compressor 111 is introduced, via the four-way valve 112, into the outdoor heat exchanger 113 that functions as a condenser. This high-pressure gaseous refrigerant undergoes heat exchange, through the outdoor heat exchanger 113, with outdoor air, whose temperature is lower than the refrigerant temperature, to be condensed to a high pressure state. Here, the outdoor fan 116 is driven by an outdoor fan motor (not shown), and serves to forcibly ventilate the outdoor air.

As the high-pressure condensed gaseous refrigerant passes through the EEV 114, it turns to low-temperature and low-pressure liquid refrigerant by throttling, and is conveyed to the indoor heat exchanger 121 of the indoor unit 120. Here, the indoor fan 123 is driven by an indoor fan motor (not shown), and serves to forcibly ventilate the indoor air.

Next, the refrigerant in a liquid state is evaporated through heat exchange with indoor air at the indoor heat exchanger 121 which functions as an evaporator. After evaporation, the low-temperature and low-pressure gaseous refrigerant flows back to the outdoor unit 110 along a circulation line, in which it passes through the four-way valve 112 and is introduced again into the compressor 111 via the accumulator 115. Here, the accumulator 115 is utilized to change the refrigerant that is introduced into the compressor 111 into dry saturated vapor.

Further, during a heating operation of the typical air conditioner with the above-described configuration, the refrigerant flow direction at the four-way valve 112 is reversed, so the refrigerant flows in an opposite direction from the refrigerant flow during the cooling operation set forth above. At this time, since the indoor heat exchanger 121 functions as a condenser differently from the cooling operation, warm air is circulated again into the indoor environment by the indoor fan 123. That is, the refrigerant flow during the heating operation of the air conditioner follows the circulation line: for example, “the compressor 111→the four-way valve 112→the indoor heat exchanger 121→the EEV 114→the outdoor heat exchanger 113→the four-way valve 112→the accumulator 115→the compressor 111”.

Meanwhile, in a cooling mode, the EEV employed in the air conditioner with the refrigerant circulation line described above offers the functions of converting condensed liquid refrigerant introduced from the outdoor heat exchanger (condenser) into low-temperature and low-pressure liquid refrigerant by throttling, and then sending it to the indoor heat exchanger (evaporator); and adjusting an amount of refrigerant to be circulated. In a heating mode, it provides the like functions of the cooling mode by circulating the refrigerant in the opposite direction of the cooling mode.

Generally, in the initial operation of the air conditioner, the air conditioner starts running with the EEV being closed. That is, an initial value of the opening level of the EEV is zero pulses/sec. Since the air conditioner starts running at the definite initial value of zero pulses/sec, convenience in control of the opening level of the EEV is secured.

One of conventional methods to control the opening level of EEV is to let the air conditioner to operate with the EEV being completely closed in the initial phase of a start-up, and then to change the opening level to a reference opening level (reference opening pulse frequency) that is calculated based on an indoor heat load.

However, in the conventional method of controlling the start-up of the air conditioner in the state that the EEV is completely closed in the initial phase of the start-up, the EEV must be opened forcibly by using a separate jig at the time of refrigerant injection or for vacuum work in the production line, which not only complicates work processing but also increases the number of work processes to thereby lower productivity because.

Moreover, in case of the conventional method, whenever a refrigerant leak detected in a product being sold calls for a repair, the EEV is closed, so that a repair technician cannot inject refrigerant after vacuum work. Therefore, the technician cannot perform required tasks until he first shuts down the power during a test operation and opens the EEV to a certain degree. This pre-operational requirement causes serious inconvenience in after-sales service of the air conditioner.

Besides, according to the conventional method, a trip phenomenon is more likely to occur. That is, when the air conditioner stops momentarily due to a sudden power interruption and restarts its normal operation, sufficient torque of a compressor motor cannot be obtained because there is still a pressure difference, which causes a trip to the motor.

SUMMARY OF THE INVENTION

It is, therefore, an object of the present invention to provide a method for controlling an EEV of an air conditioner, which opens the EEV completely at the same time as power is applied, closes the EEV completely in response to an operation start signal, and adaptively controls the opening level of the EEV based on a calculated reference opening pulse frequency (reference opening level).

In accordance with an aspect of the invention, there is provided a method for controlling an electronic expansion valve (EEV) in an air conditioner using a compressor, the method including the steps of:

(a) opening the EEV completely when a power is applied to the air conditioner in stand-by mode;

(b) closing the EEV completely when the air conditioner starts a cooling or a heating operation;

(c) calculating an indoor heat load based on an indoor and an outdoor temperature and a difference between the indoor temperature and a target temperature;

(d) calculating a reference opening pulse frequency of the EEV based on the calculated indoor heat load, the indoor and the outdoor temperature, and a reference operating frequency of the compressor; and

(e) controlling in a stepwise manner an opening pulse frequency of the EEV based on the reference opening pulse frequency of the EEV until it reaches the reference opening pulse frequency of the EEV.

BRIEF DESCRIPTION OF THE DRAWINGS

The above and other objects and features of the present invention will become apparent from the following description of embodiments, given in conjunction with the accompanying drawings, in which:

FIG. 1 shows an overall structural view of a typical air conditioner system;

FIG. 2 illustrates a block diagram of an operation control device of an air conditioner suitable for applying thereto a method for controlling an EEV in the air conditioner in accordance with an embodiment of the present invention;

FIG. 3 is a flowchart illustrating a procedure for adaptively controlling an opening level of the EEV in the air conditioner in accordance with the present invention; and

FIG. 4 depicts a timing chart for explaining a procedure of gradually conducting a start-up control of the EEV in the air conditioner with the elapse of time in accordance with the present invention.

DETAILED DESCRIPTION OF THE EMBODIMENT

Hereinafter, embodiments of the present invention will be described in detail with reference to the accompanying drawings.

As will be described below, unlike the conventional method which operates an air conditioner with the EEV being completely closed in the initial phase of a start-up of the air conditioner and then changes the opening level of the EEV to a reference opening level calculated on the basis of an indoor heat load, etc., the present invention controls an opening level of the EEV in the air conditioner in a manner that an EEV of an air conditioner is completely open in response to power-on, completely closed when an operation start signal is inputted, and then controlled adaptively (i.e., in a stepwise manner or gradually) based on a reference opening pulse frequency (reference opening level) calculated on the basis of indoor heat load, etc. Using this technical means makes it easier to accomplish the object of the invention.

FIG. 2 illustrates a block diagram of an operation control device of an air conditioner suitable for applying thereto a method for controlling an EEV in the air conditioner in accordance with an embodiment of the invention. The operation control device shown in FIG. 2 includes an indoor temperature sensor 202, an outdoor temperature sensor 204, a manipulation block 206, a control block 208, a memory block 209 and an EEV driving block 210.

Referring to FIG. 2, the indoor temperature sensor 202 is installed at, e.g., a specific position of an indoor unit 120 shown in FIG. 1, to measure an indoor temperature. The measured indoor temperature is then forwarded to the control block 208. Similarly, the outdoor temperature sensor 204 is installed at, e.g., a specific position of an outdoor unit 110 shown in FIG. 1, to measure an outdoor temperature. The measured outdoor temperature is then delivered to the control block 208.

The manipulation block 206 has a plurality of manipulation keys that are arranged for allowing a user to input various operation information such as power-on, operation mode (cooling operation mode, heating operation mode, etc.), target temperature, target air volume and the like. Various operation information received from the user is transferred to the control block 208.

The control block 208 includes, e.g., a microprocessor and the like, to carry out the overall operation control of the air conditioner, and determines calibration coefficients for the indoor temperature, for the outdoor temperature and for a difference between the indoor temperature and the target temperature. For this, in the memory block 209, pre-stored in the form of tables are calibration coefficients for the indoor temperature, for the outdoor temperature and for a difference between the indoor temperature and the target temperature.

Further, the control block 208 calculates the indoor heat load based on a preset cooling capacity, a preset heating capacity, and each of the calibration coefficients determined; and then calculates a reference opening pulse frequency of the EEV in each mode (i.e., reference opening pulse frequencies in the cooling and the heating mode) based on the calculated indoor heat load, the indoor and the outdoor temperature, and a reference operating frequency of a compressor. The control block 208 adaptively (in a stepwise manner or gradually) controls the opening level of the EEV on the basis of the calculated reference opening pulse frequency. Here, the cooling and the heating capacity are fixed values depending on the capacity of the indoor unit.

Moreover, for the control according to the present invention, the control block 208 completely opens the EEV having been closed at the same time as the power is applied, completely closes the EEV when an operation start signal is inputted by a user (or by an advance setting), and in a stepwise manner or gradually controls the opening level of the EEV based on the calculated reference opening pulse frequency. More details on this procedure will be provided with reference to FIG. 3 later.

Furthermore, the control block 208 carries out its normal functions, i.e., selectively generating any of control signals for driving the indoor fan, the outdoor fan, the compressor and so forth, and providing the same to each corresponding component.

Lastly, the EEV driving block 210 controls the opening level of the EEV 114 shown in FIG. 1, in response to opening level control signals provided from the control block 208. More concretely, the EEV driving block 210 completely opens the EEV 114 in response to an open control signal from the control block 208 when a power is turned on; completely closes the EEV 114 in response to a close control signal from the control block 208 when an operation start signal is inputted; and in a stepwise manner or gradually increases the opening level of the EEV up to the reference opening level under the control of the control block 208.

Now, a stepwise procedure for control of the opening level of the EEV in accordance with the present invention will be described referring to the operation control device of the air conditioner having the configuration described above.

FIG. 3 is a flowchart illustrating a method for adaptively controlling an opening level of an EEV in an air conditioner in accordance with the present invention.

Referring to FIG. 3, when a power-on signal is inputted by a user while an air conditioner is on a stand-by mode (stand-by power mode), item, if a power-on signal is inputted from the manipulation block 206 (steps S302 and S304), the control block 208 generates, in response to the power-on signal, an open control signal for completely opening the EEV 114 shown in FIG. 1, and sends the generated open control signal to the EEV driving block 210. In response to this, the EEV driving block 210 generates a driving signal for completely opening the EEV 114 to thereby completely open the EEV 114 (step S306). At this time, because the EEV 114 is fully open, a difference in pressure between the indoor and the outdoor unit disappears and thus pressure equilibrium is realized. Through this, it becomes possible to prevent a trip phenomenon, which occurs due to insufficient torque of a compressor motor caused by the pressure difference.

Thereafter, with the EEV 114 being completely open, the control block 208 checks whether an operation start signal is inputted (step S308) As a result of the checking, if the operation start signal is inputted, the control block 208 generates a close control signal for completely closing the EEV 114 and sends the generated close control signal to the EEV driving block 210. In response to this, the EEV driving block 210 generates a driving signal for completely closing the EEV 114, thereby fully closing the EEV 114 (step S310). At this time, an opening pulse frequency of the EEV 114 is zero pulse/sec (initial value).

Next, the indoor temperature sensor 202 measures an indoor temperature (indoor air temperature) T_(ai) and provides it to the control block 208, and the outdoor temperature sensor 204 measures an outdoor temperature (outdoor air temperature) T_(ao) and offers it to the control block 208 (step S312).

In response to the above, the control block 208 determines calibration coefficients FT_(ai) for the indoor temperature, FT_(ao) for the outdoor temperature and FdT for a difference dT between the indoor temperature and a target temperature (user set temperature) with reference to tables of calibration coefficients pre-stored in the memory block 209 (step S314). Here, each of the calibration coefficients is used for adjusting the reference opening level of the EEV 114.

For the above purpose, the memory block 209 stores calibration coefficients made in the form of table. For example, those calibration coefficients may be defined as shown in Tables 1 to 3.

TABLE 1 Cooling Mode Heating Mode T_(ai) FT_(ai) T_(ai) FT_(ai) 33 < T_(ai) 1.30 26 ≦ T_(ai) 1.20 31 < T_(ai) ≦ 33 1.20 24 ≦ T_(ai) < 26 1.15 29 < T_(ai) ≦ 31 1.15 22 ≦ T_(ai) < 24 1.10 28 < T_(ai) ≦ 29 1.10 18 ≦ T_(ai) < 22 1.00 26 < T_(ai) ≦ 28 1.00 14 ≦ T_(ai) < 18 0.95 25 < T_(ai) ≦ 26 0.90 T_(ai) < 14 0.90 23 < T_(ai) ≦ 25 0.85 21 < T_(ai) ≦ 23 0.80 T_(ai) ≦ 21 0.70

TABLE 2 Cooling Mode Heating Mode T_(ao) FT_(ao) T_(ao) FT_(ao) 45 < T_(ao) 1.30 18 ≦ T_(ao) 1.15 43 < T_(ao) ≦ 45 1.20 11 ≦ T_(ao) < 18 1.10 39 < T_(ao) ≦ 43 1.15  4 ≦ T_(ao) < 11 1.00 37 < T_(ao) ≦ 39 1.10 0 ≦ T_(ao) < 4 0.90 33 < T_(ao) ≦ 37 1.00 −4 ≦ T_(ao) < 0  0.85 31 < T_(ao) ≦ 33 0.95 T_(ao) < −4 0.80 27 < T_(ao) ≦ 31 0.90 25 < T_(ao) ≦ 27 0.85 T_(ao) ≦ 25 0.80

TABLE 3 Cooling Mode Heating Mode dT FdT dT FdT 2.0 < dT 1.0 3 ≦ dT 0 1.0 < dT ≦ 2.0 0.8 2.5 ≦ dT < 3   0.1 0.0 < dT ≦ 1.0 0.5 2.0 ≦ dT < 2.5 0.2  −1 < dT ≦ 0.0 0.1 1.5 ≦ dT < 2.0 0.3 dT ≦ −1.0 0.0 1.0 ≦ dT < 1.5 0.5 0.5 ≦ dT < 1.0 0.7 0.0 ≦ dT < 0.5 0.8 dT < 0.0 1

Table 1 shows an example list of calibration coefficients for indoor temperatures in both cooling and heating operation modes, and Table 2 represents an example list of calibration coefficients for outdoor temperatures in both cooling and heating operation modes. Table 3 depicts an example list of calibration coefficients for differences between the indoor temperatures and target temperatures in both cooling and heating operation modes.

Subsequently, the control block 208 calculates indoor cooling/heating load Q by Equation 1 based on the preset cooling capacity Q_(c), the preset heating capacity Q_(h), the calibration coefficient FT_(ai) for the indoor temperature, the calibration coefficient FT_(ao) for the outdoor temperature, and the calibration coefficient FdT for the difference between the indoor temperature and the target temperature (step S316).

$\begin{matrix} {Q = \left\{ \begin{matrix} {Q_{c} \times {FT}_{ai} \times {FT}_{ao} \times {FdT}} & \left( {{Cooling}\mspace{14mu} {mode}} \right) \\ {Q_{h} \times {FT}_{ai} \times {FT}_{ao} \times {FdT}} & \left( {{Heating}\mspace{14mu} {mode}} \right) \end{matrix} \right.} & {{Equation}\mspace{14mu} 1} \end{matrix}$

Next, the control block 208 calculates a reference opening pulse frequency P_(b,c) of the EEV in a cooling mode and a reference opening pulse frequency P_(b,h) of the EEV in a heating mode by using Equations 2 and 3, respectively, based on the indoor heat load Q obtained from Equation 1, a reference operating frequency F_(b) of the compressor, the indoor temperature T_(ai), and the outdoor temperature T_(ao) (step S318). Here, the indoor and the outdoor temperature are required to be calculated in absolute temperatures. Or, errors may occur in substituting them to Equations 2 and 3 when they are sub-zero temperatures.

P _(b,c)=0.0002543×T _(ai) ^(2.081) ×F _(b) ^(0.4405)  Equation 2

P _(b,h) =T _(ai) ⁻⁴⁴³⁷ ×T _(ao) ⁴³⁶⁹ ×F _(b) ⁰⁴⁴⁹ ×Q ⁰⁴⁷⁴  Equation 3

In general, the opening pulse frequency of the EEV in the air conditioner approximately ranges from 70 pulses/sec to 280 pulses/sec. Therefore, during the operation of the air conditioner, the control block 208 calculates the reference opening pulse frequency of the EEV within the range from about 70 pulses/sec to 280 pulses/sec, and adjusts the opening level of the EEV based on the calculated reference opening pulse frequency.

That is, in accordance with the invention, after completely opening the EEV when a power is turned on and completely closing it again when an operation start signal is inputted, the reference opening pulse frequency for adjusting the opening level of the EEV is calculated through the above-described procedure.

Next, the control block 208 gradually controls or in a stepwise manner the opening level of the EEV by using the reference opening pulse frequency. For example, as shown in FIG. 4, the opening level of the EEV can be controlled in a stepwise manner through a four-stage EEV opening pulse control (e.g., four stages having operating pulse frequencies of 0.7×P_(b), 0.8×P_(b), 0.9×P_(b) and 1.1×P_(b), respectively, and each stage having a duration of one minute) until it reaches the reference opening pulse frequency P_(b) (step S320). In other words, the procedure of the invention enters a steady state control after a start-up control of the EEV is performed in four minutes by increasing the opening pulse frequency at every one minute based on the reference opening pulse frequency.

More specifically, in the first minute after an input of the operation start signal (a first stage), the start-up control is carried out at a first start-up pulse frequency which is obtained by multiplying the reference opening pulse frequency by 0.7. In the second minute (a second stage), the start-up control is conducted at a second start-up pulse frequency which is obtained by multiplying the reference opening pulse frequency by 0.8. In the third minute (a third stage), the start-up control is performed at a third start-up pulse frequency which is obtained by multiplying the reference opening pulse frequency by 0.9. Lastly, in the fourth minute (a fourth stage), the start-up control is carried out at a fourth start-up pulse frequency which is obtained by multiplying the reference opening pulse frequency by 1.1 (which is a higher opening pulse frequency pulse than the reference opening pulse frequency). After the four minutes (i.e., after performing the four-stage start-up control in a stepwise manner), the steady state control is carried out at the reference opening pulse frequency.

Here, the reason for setting the opening pulse frequency of the EEV at the fourth stage to be higher than the reference opening pulse frequency P_(b) is to prevent a rapid increase in a discharge pressure of the compressor in case the operating frequency of the compressor reaches its maximum level only after three minutes following the start-up of the compressor in overload or full load condition.

Therefore, in accordance with the present invention, since the EEV is completely open when a power is turned on, a separate jig (for forcibly opening the EEV) for injection of refrigerant in the production line is no longer needed. This leads to a simplified work processing as well as a decrease in work processes, thereby increasing product yield.

In addition, during a repair service upon occurrence of a refrigerant leak in a product being sold, the EEV is completely open when only a power is turned on, and thus a repair technician can more easily connect a vacuum pump to inject refrigerant, thereby realizing quick after-sales service.

Moreover, in case the air conditioner stops momentarily due to a sudden power interruption and restarts its normal operation (returning to power-on mode), the EEV automatically opens to full extent to maintain pressure equilibrium. Therefore, a trip phenomenon that may occur due to insufficient torque of a compressor motor caused by difference in pressure can be effectively prevented.

Meanwhile, in accordance with the embodiment of the present invention, although the start-up of the EEV is controlled by changing in a stepwise manner the opening level of the EEV until it reaches the reference opening pulse frequency through four stages (e.g., 0.7×P_(b), 0.8×P_(b), 0.9×P_(b) and 1.1×P_(b)), the embodiment is only for illustrative purposes, and the present invention is not limited thereto. If needed or depending on application, the opening level of the EEV may be classified into and controlled through more than four stages (e.g., five, six, seven, eight stages and so on), and it is apparent that the start-up operation of the EEV can be controlled even more smoothly through the use of the above scheme.

Furthermore, in accordance with the embodiment of the present invention, although the air conditioner is driven evenly for one minute at each of the four stages of the opening level of the EEV, the embodiment is only for illustrative purposes, and the present invention is not limited thereto. It is apparent that the time period can be increased or decreased in consideration of various factors, such as, surrounding environment of the air conditioner. It is also noted that the running time of the air conditioner at each stage can be set differently whenever needed or depending on application.

Besides, in accordance with the embodiment of the present invention, although calibration coefficients for an indoor temperature, for an outdoor temperature and for a difference in temperature (i.e., a difference between the indoor temperature and the target temperature) are read out from the pre-stored tables, the embodiment is only for illustrative purposes, and the present invention is not limited thereto. It is apparent that the calibration coefficients may be calculated in real time mode, instead of being pre-stored in the tables.

As described above, unlike the conventional method which operates an air conditioner with the EEV being completely closed in the initial phase of a start-up of the air conditioner and then changes the opening level of the EEV to a reference opening level calculated on the basis of an indoor heat load, etc., the present invention controls an opening level of an EEV in an air conditioner in a manner that the EEV of the air conditioner is completely open in response to power-on, completely closed when an operation start signal is inputted and then controlled adaptively (in a stepwise manner or gradually) based on a reference opening pulse frequency (a reference opening level) calculated on the basis of indoor heat load, etc. In accordance with the present invention, a simplified processing in manufacturing procedure associated with refrigerant injection and a quick after-sales service can be realized. Further, a trip phenomenon that may occur due to insufficient torque of a compressor motor caused by a difference in pressure in restart-up after stop can be effectively prevented.

While the invention has been shown and described with respect to the embodiments, it will be understood by those skilled in the art that various changes and modification may be made without departing from the scope of the invention as defined in the following claims. 

1. A method for controlling an electronic expansion valve (EEV) in an air conditioner using a compressor, the method comprising the steps of: (a) opening the EEV completely when a power is applied to the air conditioner in stand-by mode; (b) closing the EEV completely when the air conditioner starts a cooling or a heating operation; (c) calculating an indoor heat load based on an indoor and an outdoor temperature and a difference between the indoor temperature and a target temperature; (d) calculating a reference opening pulse frequency of the EEV based on the calculated indoor heat load, the indoor and the outdoor temperature, and a reference operating frequency of the compressor; and (e) controlling in a stepwise manner an opening pulse frequency of the EEV based on the reference opening pulse frequency of the EEV until it reaches the reference opening pulse frequency of the EEV.
 2. The method of claim 1, wherein the step (e) includes the steps of: (e1) controlling the opening pulse frequency of the EEV at a first start-up pulse frequency for a first time period; (e2) controlling the opening pulse frequency of the EEV at a second start-up pulse frequency for a second time period; (e3) controlling the opening pulse frequency of the EEV at a third start-up pulse frequency for a third time period; (e4) controlling the opening pulse frequency of the EEV at a fourth start-up pulse frequency for a fourth time period; and (e5) controlling the opening pulse frequency of the EEV at the reference opening pulse frequency.
 3. The method of claim 2, wherein the first to the third start-up frequency are lower than the reference opening pulse frequency in an increasing order and the fourth start-up pulse frequency is greater than the reference opening pulse frequency.
 4. The method of claim 2, wherein the first to the fourth time period have an identical time duration.
 5. The method of claim 2, wherein the fourth start-up pulse frequency is determined to keep an increasing rate of a discharge pressure of the compressor to be lower than a specific level even if an operating frequency of the compressor reaches its maximum level. 